The cellular phone as one type of the mobile radio apparatus is widely spreading nowadays. As the cellular phone, various types of the cellular phone have already been developed. Out of them, the compact folding cellular phone whose portability can be enhanced by folding upper and lower cases when not used is widely used. In this foldable mobile radio apparatus, improvements in size reduction and multiple functions are proceeding. Also, as one of recent improvements in multiple functions, use of the built-in antenna is advanced to improve the design quality.
As an example, as disclosed in JP-A-2002-335180, there is the foldable mobile radio apparatus having such a configuration that the flexible cable is connected to the shield box in the upper case, and then the dipole antenna having the upper shield box and the ground pattern, which is the conductive pattern on the circuit board at a ground potential of the lower case, as radiation elements is operated by exciting directly the upper shield box. According to this configuration, the wide-band and high-gain antenna performance can be achieved since an effective area of the antenna can be realized widely.